1. Field of the Invention
The present invention relates to a tunable resonator, and more particularly, to a tunable resonator which changes a resonance frequency of a film bulk acoustic resonator (FBAR), thereby fulfilling a multiband operation.
2. Description of the Related Art
In recent, wireless communication technologies have rapidly progressed to realize a so-called ubiquitous society. Also, high-speed and high-advanced wireless communication environments and compact-sized wireless communication terminals such as mobile terminals have been increasingly demanded. With this development of wireless communication technologies, the radio frequency-micro electro mechanical system (RF-MEMS) technology makes it possible to realize the high-advanced and compact-sized wireless device. The RF-MEMS technology refers to a technology that manufactures a mechanical micro structure mainly on a semiconductor substrate, thereby realizing high performance and compact-sizing that could not be obtained by a semiconductor device. Example of the devices using the RF-MEMS technology is a tunable capacitor, a switch, a film bulk acoustic resonator (FBAR).
The FBAR refers to a resonator that comprises a lower electrode, a piezoelectric layer, and an upper electrode which are laminated in sequence. If an electric energy is applied to both the electrodes, an acoustic wave is generated due to the piezoelectric effect and accordingly a resonance is generated.
FIG. 1 is a view illustrating a conventional RF front end. Referring to FIG. 1, a conventional RF duplexer has to have a plurality of filters to transmit and receive information using various frequency bands. These filters generally use a FBAR. In the filters using a general FBAR, a frequency range is determined based on the thickness of a resonator comprising a piezoelectric layer and a plurality of electrode layers. However, the filter using a general FBAR has a limitation in the etching of thickness and the frequency cannot be tuned if it has been once tuned. Therefore, there is a problem that a multiband operation cannot be fulfilled. Also, since the plurality of filters is required as shown in FIG. 1, it is difficult to realize a compact-sized device.